Recently, a lighting apparatus for vehicle is increasingly utilized, in which a light emitting diode is used for a light source, such as a vehicle headlight, a vehicle interior lamp, a vehicle taillight, an auxiliary lamp or a daytime running light. The lighting apparatus for vehicle is configured to make a light-emitting-diode-driving device perform lighting drive of the light source including the light emitting diode.
As this type of light-emitting-diode-driving device, there has been known one example shown in FIG. 14, which includes a failure determination circuit 105 configured to determine presence or absence of a short circuit in a light source 102 (e.g., see JP2009-111035A (hereinafter, referred to as a “document 1”)).
A light-emitting-diode-driving device A in the document 1 includes a driving circuit 103 configured to convert electric power supplied from a power supply 108, and output a boosted DC voltage. The driving circuit 103 is configured to apply the boosted DC voltage to the light source 102, in which a plurality of light emitting diodes 101 are connected in series, to turn on the light source 102. The light-emitting-diode-driving device A further includes a voltage detection circuit 104 configured to detect a voltage across the light source 102. The voltage detection circuit 104 is configured to detect the voltage across the light source 102 with voltage detection resistors 104a and 104b that are connected in series to each other and are connected in parallel to the light source 102. The driving circuit 103 is configured to keep electric power to be supplied to the light source 102 at prescribed constant electric power by performing PWM (Pulse Width Modulation) control. The light-emitting-diode-driving device A further includes a current detection circuit 107 configured to detect, with a current detection resistor 107a, a current flowing through the light source 102. Further, the light-emitting-diode-driving device A includes a display unit 106 configured to display a result of presence or absence of a short circuit in the light source 102, determined by the failure determination circuit 105.
Here, this type of light-emitting-diode-driving device is required to detect more accurately a short circuit failure in a light source including a light emitting diode. However, such a requirement is not satisfied only with the configuration of the light-emitting-diode-driving device in the document 1. Therefore, this type of light-emitting-diode-driving device is required to be further improved.